The present invention relates generally to an anti-skid control system for use in vehicle hydraulic braking systems, and more particularly to such an anti-skid control system with a fail-safe control function for providing a compensation for a safe braking operation in the occurrence of failures of a hydraulic braking device.
Various anti-skid control systems for use in motor vehicles have hitherto been proposed which optimize a hydraulic braking pressure under control of a control unit with a view to providing a more effective and safer braking action in braking the vehicle under varying road suface conditions.
The anti-skid control system would require a fail-safe control function because of the necessity to ensure that the vehicle braking operation can be performed irrespective of the occurrence of failures of a hydraulic braking device. Japanese Patent Provisional Publication No. 57-84254, for example, discloses an anti-skid control system including an vehicle braking compensation device for when failures exist with the hydraulic pressure developing device comprising a hydraulic pressure pump and an accumulator. However, this prior art system does not take into account the vehicle braking compensation in the occurrence of failures of a control valve for controlling the hydraulic pressure applied to the inside of a wheel braking cylinder. Thus, a further improvement would be required from the viewpoint of increase in reliability and safety with respect to the vehicle hydraulic braking system.